Amazing series. You don't need to have any knowledge about the League of Legends game to enjoy. If you do have some knowledge, it's like a cluster of easter eggs in an open field.
All of the characters, even side characters, are very well flushed out and enjoyable. Each personality and belief is consistent with the character. Characters that are irrelevant have little screen time and vice versa. Plot has very good pacing and many points of view that are opposing to each other. Lots of action. None of the typical "evil super villain monologue" to waste time. Good music. Good animation.
There are some scenes that could be removed and are a little necessary but overall 9.5/10.